Adjustment mechanism for altering height of baby playpen

1. An adjustment mechanism for altering a height of a baby playpen from a ground to a bottom of the baby playpen, the adjustment mechanism comprising:

a foldable skeleton, wherein the foldable skeleton is formed by assembling an upper foldable surrounding set, a bottom frame set and a plurality of vertical poles which are disposed between the upper foldable surrounding set and the bottom frame set, and each of the vertical poles has a guide slot of which a sidewall has a plurality of positioning holes;

a seat fabric, slideably put on the foldable skeleton to construct a plurality of side surface and a bottom surface for forming an accommodation space; and

a height adjustment positioning mechanism disposed between the foldable skeleton and the seat fabric thereby altering the height of the bottom surface from the ground by adjusting the seat fabric, and the height adjustment positioning mechanism comprising:

a slide base which is connected with the seat fabric and can slide upwards and downwards along the guide slot; and

a positioning pole slidably disposed between the vertical pole and the slide base, wherein the height of the bottom surface from the around is fixed by engaging the positioning pole with one of the positioning holes.

2. The adjustment mechanism of claim 1 , wherein a plurality of positioning portions are disposed on the vertical poles.

3. The adjustment mechanism of claim 1 , wherein an elastic element is disposed between the positioning pole and the slide base for keeping the engagement between the positioning pole and the positioning hole.